Research Of Interlayer Exchange Coupling In MgO Magnetic Tunnel Junctions

The interlayer exchange coupling in magnetic multilayers plays an important role in GMR and TMR.If the interlayer exchange coupling can be controlled by an electric field to control the high or low magnetoresistance state of GMR or TMR,it will undoubtedly be able to greatly reduce the energy consumption while improving stability.In this paper,we investigate the interlayer exchange coupling in CoFeB/MgO/Py tunnel junctions and CoFeB/MgO/CoFeB tunnel junctions.When using insulator as the spacer layer in magnetic multilayers,the interlayer exchange coupling may change from ferromagnetic(antiferromagnetic)to antiferromagnetic(ferromagnetic)at a critical point without an oscillatory phenomenon.However,in this paper,we find that there is an oscillatory interlayer exchange coupling in the CoFeB(8.4nm)/MgO(t)/Py(9.3 nm)MTJs when the thickness of MgO is in the range of 0.34 nm ?0.45 nm,as the thickness of MgO increases.This may be related to the antiferromagnetic material CoO in CoFe B.Besides,when increasing the thickness of Py,we also find an oscillatory interlayer exchange coupling in the MTJs and the period is about 1.2 nm.If only the thickness of CoFeB is changed,the ferromagnetic coupling will only occur when the thickness of CoFeB is approximately in the range of 8.40 nm to 8.96 nm due to the different electronic structure of CoFeB and Py.If the thickness of MgO exceeds 0.45 nm,only antiferromagnetic coupling can be observed.There is no ferromagnetic coupling when changing the thickness of MgO or Py.In the CoFeB(3.36nm)/MgO(t)/CoFeB(4.2nm)tunnel junctions,only antiferromagnetic coupling can be observed while increasing the thickness of Mg O.However,in CoFeB(3.08nm)/Mg O(0.39nm)/CoFeB(t)tunnel junctions,when changing the thickness of CoFeB,the interlayer exchange coupling may change from antiferromagnetic coupling to ferromagnetic and back to antiferromagnetic coupling again.In addition,applying an electric field perpendicular to the antiferromagnetic coupling MTJs can significantly enhance the amplitude of antiferromagnetic coupling.On the contrary,the amplitude of antiferromagnetic coupling can be reduced when reversing the sign of the electric field.